<p>The objectives and intended uses of the proposed IEEE P1149.5 Module Test and Maintenance Bus standard are reviewed. Design-for-test features being used in component designs to aid in component, board, subsystem, and system test and maintenance are reviewed. The relationship of the IEEE P1149.5 MTM bus to other test buses is outlined, and the operation protocol is described. Extensions of the standard to meet the needs of specifications are discussed.</p>